1. Field of the Invention
The present invention relates to a spring biasing device and, more particularly, to a safety means for a spring biasing device.
2. Description of the Prior Art
Many mechanisms, such as the brake actuator shown in U.S. Pat. No. 3,508,470 to Swander, Jr. et al, use a spring biasing device to urge a shaft in a particular direction or provide a movement-resisting force on the shaft. Valve actuators exemplify one type of mechanism in which spring biasing devices have been found particularly useful. U.S. Pat. Nos. 1,517,728 to Heath; 2,796,856 to Gratzmuller; 3,175,473 to Boteler et al; 3,591,127 to Luger et al; 3,727,523 to Gulick; 3,824,901 to Shafer; 4,087,074 to Massey et al; and 4,261,546 to Cory et al and French patent 1,425,399 show various configurations of spring biasing devices used with valve actuators. U.S. Pat. No. 2,198,026 to Farmer shows another application for a spring biasing device, a mechanism to direct a signal horn and U.S. Pat. Nos. 2,402,400 to Hewitt et al shows a spring biased regulating device.
The valve actuators described in the Gulick and Cory et al patents illustrate particularly well both the advantages and dangers inherent in known self-contained spring biasing devices that are easily detachable from the actuator. The spring biasing device shown in those patents comprises a cylinder that is detachably secured to the actuator. The front end plate of the cylinder removably attaches the spring biasing device to the actuator. The actuator power shaft passes through an opening in the front end plate of the cylinder and abuts a bearing plate inside the cylinder. As the shaft pushes the bearing plate toward the rear end plate of the cylinder, it compresses a spring between the bearing plate and the rear end plate. The actuator power shaft abuts the bearing plate, but is not connected to it. That makes the actuator very versatile because the entire spring biasing device can be quickly removed from the actuator and replaced with another merely by disconnecting from the actuator the front end plate of the cylinder of one device and connecting in its place the front end plate of the cylinder of another device. By the same token, failure of the connection between the cylinder and the actuator allows the spring to launch the entire spring biasing device from the actuator. Because actuators like that shown in the Cory et al patent routinely use springs capable of generating forces well in excess of 2000 pounds and spring biasing devices weighing over 100 pounds, they can be potentially very dangerous.
Connecting the actuator power shaft to the bearing plate will greatly diminish the potential danger inherent in such an actuator. In many spring biasing devices the shaft does attach to the bearing plate. For example, U.S. Pat. No. 3,903,704 to Spiridonov shows such an arrangement in a spring biasing device used to anchor a pipeline. And the Shafer patent shows a valve actuator in which an extension of the actuator power shaft is welded to the bearing plate. But if the power shaft and bearing plate of an actuator like that shown in the Gulick or Cory et al patent are connected as shown in the Spiridonov or Shafer patent, the actuator's versatility is largely lost.